The specific aims of this project are to determine whether vitamin A or the synthetic retinoids administered systemically can act to delay or inhibit carcinogenesis of oral mucous membrane. Two well established oral mucosal tumor systems will be used: the hamster buccal pouch epidermoid carcinoma induced by DMBA in oil and the hamster tongue epidermoid carcinoma induced by DMBA in acetone. Delayed carcinogenesis will be evaluated by delayed appearance histologically of dysplasia, carcinoma-in-situ and frank invasive epidermoid carcinoma. Retinoids studied will be vitamin A, retinyl acetate, retinyl palmitate, and 13-cis-retinoic acid. The presence of retinoids in the oral mucosa, dysplastic oral epithelium and carcinoma will be studied by autoradiographic techniques and by chemical techniques. Aryl hydrocarbon hydroxylase activity of tissues will also be studied.